This invention relates generally to oleochemical raw materials and, more particularly, to a new process for the homogeneously chemical oligomerization of unsaturated fatty compounds with olefins.
The derivatization of renewable raw materials, more particularly fats and oils, leads to economically and industrially interesting products such as, for example, plasticizers, lubricants and the like. In this connection, the use of homogeneously soluble transition metal compounds as catalysts has proved successful because high selectivities can be obtained with such catalysts, even under mild reaction conditions.
Interesting products include internally alkyl-branched fatty acid derivatives whose outstanding physical properties (for example low melting point, high chemical stability, low viscosity) make them potentially suitable for a number of applications [cf. S. Gronowitz et al. Lipids, 28,889 (1993) or D. V. Kinsman in: Fatty Acids in Industry (eds. R. W. Johnson, E. Fritz), Marcel Dekker, Inc., New York, 1989, p. 233]. Branched fatty acid derivatives may therefore be regarded as sought-after raw materials, for example for the lubricant or cosmetics industry. Where the derivatives are readily biodegradable, they could be used above all as “lost” lubricating oils.
On an industrial scale, branched fatty derivatives accumulate in particular in the Guerbet reaction in which fatty alcohols are dimerized at elevated temperatures in the presence of alkalis to form 2-alkyl-branched alcohols. Another method of producing branched fatty compounds is the dimerization of unsaturated fatty acids where complex mixtures of partly cyclic dimers are obtained in addition to methyl-branched monomer fatty acids. Finally, there is hydrocarboxylation or the Koch reaction in which 2,2-dimethyl-branched fatty compounds are obtained.
Towards the end of the eighties, Behr et al. produced internally alkyl-branched fatty acid derivatives by the rhodium-catalyzed addition of ethene onto linoleic or conjuene fatty acid esters using chloroform or n-hexane as solvent. A corresponding overview can be found in Fat Sci. Technol. 93, 20 (1991) and in EP 0 511 982 B1 (Henkel). The reaction is schematized below: 
Besides single adducts, multiple adducts, i.e. adducts with a molar ratio of linoleic acid derivative to ethene of 1:1 to 1:3, are also consecutively formed at 80 to 100° C. and under pressures of 10 to 30 bar. Rhodium/olefin complexes and, above all, rhodium trichloride trihydrate are recommended as suitable catalysts. The homogeneous rhodium catalyst could not be re recycled without losses of activity.
EP 0 621 257 B1 (IFP) also describes a process for the production of double-branched fatty acid derivatives in which the oligomerization of linoleic acid methyl ester is carried out in chloroform as solvent in the presence of ionic rhodium complexes. EP 0 894 785 A1 and EP 0 976 715 A1 (IFP) both also relate to processes for the co-oligomerization of polyunsaturated fatty compounds with olefins in which nickel complexes are used together with ethyl aluminium chloride.
Although the yields obtained in known processes may be regarded as satisfactory, although still in need of improvement, industrial-scale operation has so far been unsuccessful because reliable, quantitative and industrially simple removal of the valuable, homogeneously dissolved transition metal catalyst from the reaction mixture has not yet been possible, especially since removal by distillation is unworkable on account of the high boiling points of the branched fatty compounds and the limited heat resistance of the catalysts.
Accordingly, the problem addressed by the present invention was to provide an improved process for the production of branched fatty compounds which would be distinguished from the prior art by simple, reliable and quantitative removal of the catalyst for at least equally high yields and selectivities.